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| 型號： | LT3957IUHE#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, PQCC36 |
| 封裝： | 5 X 6 MM, LEAD FREE, PLASTIC, QFN-36 |
| 文件頁數(shù)： | 11/28頁 |
| 文件大?。?/td> | 359K |
| 代理商： | LT3957IUHE#PBF |
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LT3957
19
3957f
APPLICATIONS INFORMATION
SEPIC CONVERTER APPLICATIONS
The LT3957 can be congured as a SEPIC (single-ended
primary inductance converter), as shown in Figure 1. This
topology allows for the input to be higher, equal, or lower
than the desired output voltage. The conversion ratio as
a function of duty cycle is:
VOUT + VD
VIN
= D
1D
in continuous conduction mode (CCM).
In a SEPIC converter, no DC path exists between the input
and output. This is an advantage over the boost converter
for applications requiring the output to be disconnected
from the input source when the circuit is in shutdown.
Compared to the yback converter, the SEPIC converter
has the advantage that both the power MOSFET and the
output diode voltages are clamped by the capacitors (CIN,
CDC and COUT), therefore, there is less voltage ringing
across the power MOSFET and the output diodes. The
SEPIC converter requires much smaller input capacitors
than those of the yback converter. This is due to the fact
that, in the SEPIC converter, the current through inductor
L1 (which is series with the input) is continuous.
SEPIC Converter: Switch Duty Cycle and Frequency
For a SEPIC converter operating in CCM, the duty cycle
of the main switch can be calculated based on the output
voltage (VOUT), the input voltage (VIN) and the diode
forward voltage (VD).
The maximum duty cycle (DMAX)occurswhentheconverter
has the minimum input voltage:
DMAX =
VOUT + VD
VIN(MIN) + VOUT + VD
SEPIC Converter: The Maximum Output Current
Capability and Inductor Selection
As shown in Figure 1, the SEPIC converter contains two
inductors: L1 and L2. L1 and L2 can be independent, but
can also be wound on the same core, since identical volt-
ages are applied to L1 and L2 throughout the switching
cycle.
For the SEPIC topology, the current through L1 is the
converter input current. Based on the fact that, ideally, the
output power is equal to the input power, the maximum
average inductor currents of L1 and L2 are:
IL1(MAX) =IIN(MAX) =IO(MAX)
DMAX
1DMAX
IL2(MAX) =IO(MAX)
Due to the current limit of its internal power switch,
the LT3957 should be used in a SEPIC converter whose
maximum output current (IO(MAX)) is less than the output
current capability by a sufcient margin (10% or higher
is recommended):
IO(MAX) < 1DMAX
(
)5A 0.5 ΔISW
(
)
The inductor ripple currents
ΔIL1 and ΔIL2 are identical:
ΔIL1 = ΔIL2 = 0.5 ΔISW
The inductor ripple current
ΔISW has a direct effect on the
choice of the inductor value and the converter’s maximum
output current capability. Choosing smaller values of
ΔISW
requires large inductances and reduces the current loop
gain (the converter will approach voltage mode). Accepting
larger values of
ΔISW allows the use of low inductances,
but results in higher input current ripple and greater core
losses and reduces output current capability.
Given an operating input voltage range, and having chosen
the operating frequency and ripple current in the induc-
tor, the inductor value (L1 and L2 are independent) of the
SEPIC converter can be determined using the following
equation:
L1 = L2 =
VIN(MIN)
0.5 ΔISW
DMAX
For most SEPIC applications, the equal inductor values
will fall in the range of 1μH to 100μH.
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| LT3958EUHE#PBF | SWITCHING REGULATOR, PQCC36 |
| LT3958EUHE#TRPBF | SWITCHING REGULATOR, PQCC36 |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LT3957IUHETRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch |
| LT3958 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Monolithic High Voltage Isolated Flyback Converter No External Start-Up Resistor |
| LT3958EUHE#PBF | 功能描述:IC REG MULTI CONFIG ADJ 36VQFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:250 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V 輸入電壓:2.05 V ~ 6 V PWM 型:電壓模式 頻率 - 開關(guān):2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:6-SON（1.45x1） 產(chǎn)品目錄頁面:1032 (CN2011-ZH PDF) 其它名稱:296-25628-2 |
| LT3958EUHE#PBF | 制造商:Linear Technology 功能描述:IC BOOST/FLYBACK/SEPIC/INVERT CTRL QFN36 |
| LT3958EUHE#TRPBF | 功能描述:IC REG MULTI CONFIG ADJ 36VQFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤 |
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